Biblioteques de Barcelona WiFi Auto-Login (unofficial) does not collect, transmit, or share
any data with the developer or any third party.

• Your carnet/DNI and PIN are stored locally in your browser via
  browser.storage.local, in plain text (browser extension storage is not
  encrypted). Anyone with access to your Firefox profile can read them.
• They are only ever sent to the library portal (xsf-biblioteques.diba.cat)
  when the extension submits the login form, exactly as if you typed them in.
• No analytics, telemetry, or remote code.